The present invention relates to anesthesia systems used to provide an anesthetic agent to a patient undergoing an operation.
In general, anesthesia systems are utilized in operating rooms and comprise various equipment necessary to anesthetize the patient and maintain the patient in that state until the operation is completed and it is possible to terminate the introduction of the anesthetic agent.
Such systems comprise various pressure regulators, flow control devices, gas mixing devices and vaporizers to vaporize a volatile liquid anesthetic and to introduce the anesthetic laden gases into the patient. The patient is connected to the system by means of a face mask or other device and which interfaces with the anesthesia system via a patient circuit that may typically have an inspiratory limb through which the gases are introduced into the patient and an expiratory limb that conveys the exhaled gases from the patient.
In one typical anesthesia system, the overall flow of gases to and from the patient may be in a generally closed circuit, commonly referred to as the circle system, that is, the patient is connected to a substantially closed volume supply of gases and rebreathes certain of those exhaled gases supplemented by fresh gas.
As the driving force to the circle breathing circuit, and, of course, to the patient, a ventilator is used and which basically breathes for the patient since the patient is under anesthesia and is unable to carry out the normal spontaneous breathing functions. The ventilator, therefore, provides a quantity of the gas containing a predetermined metered quantity of the anesthetic agent along with other gases such as nitrous oxide and, of course, a life sustaining percentage of oxygen.
That gas containing the anesthetic may typically be delivered through an intermediate mechanism such as a bellows. In such case, the driving gas from the ventilator does not contain the anesthetic agent but is used to simply power the bellows to collapse that bellows to deliver the aforementioned anesthetic containing gas from the bellows to the patient. Instead of drive gas, other driving means such as an electromechanical or mechanical means are also used.
In any of the aforedescribed systems, the anesthetic laden gas is delivered to the inspiratory limb of the circle patient breathing circuit and is introduced into the patient to provide anesthesia to that patient. That anesthetic gas to the inspiratory limb is provided by a source of gases, including fresh gas, oxygen and generally nitrous oxide, that is mixed to a predetermined mixture in a gas mixer and the mixed gases are then passed through an agent vaporizer where the anesthetic agent is introduced into those gases.
In the expiratory limb of the circle patient breathing circuit, as the patient exhales, the exhalation gases pass through the expiratory limb where they are recirculated back to the inspiratory limb where they are again inhaled by the patient. In this manner, the system is closed and which allows the optimum use of the rather expensive anesthetic agent. If the fresh gas added to the circuit exceeds the net of gases taken up by the patient or leaked from the circuit, the excess gases are popped off via a pop-off valve.
One difficulty with such system is that on occasion, there is a loss of gas within the system, that is, there may be a patient disconnect where one of the limbs to the patient becomes disconnected, or, alternatively, there may simply be a leak in the system such that the gas that normally is supplied to the patient is released to the atmosphere and the patient is not receiving the amount of gas intended by the clinician.
In such instances, it is incumbent on the clinician to recognize the problem and, commonly, the clinician continuously watches the movement of the bellows expansion and contraction as the patient is supplied with respiratory gases. If the bellows fails to expand to its full volume, that is, the expansion of the bellows is less than the clinician has been viewing, there is an indication that some gas is escaping from the system. Accordingly, the clinician may continually watch the bellows movement to see if there is a lessening of the expansion and note that indication as evidence of a leak in the patient circuit.
In such cases, when the clinician recognizes the problem, corrective action must be taken to reestablish the integrity of the breathing system and to restore the anesthesia machine back to the normal pattern of ventilating the patient. At the present, when the clinician does recognize the loss of integrity in the breathing system and makes the necessary correction to terminate the leak, the clinician then normally activates an oxygen flush that is present on all anesthesia machines and which sends a high flow of oxygen to the patient circuit. While that method may serve to reinflate the bellows and supply the needed gas to refill the overall breathing system, the composition of the gas then supplied is pure oxygen and the desired oxygen concentration to the patient that had been established to the patient by the clinician must be again reestablished to restore the original breathing conditions set by the clinician.